Birefringent and electrooptical properties of improper ferroelectric Cd2 (NH4)2 (SO4)3

Publisher Website
Google Scholar
Abstract
Experimental data are presented for the temperature dependences of the spontaneous birefringence and orientation of the indicatrix in the ordered phase of CAS and of their field-induced changes. These quantities are expressed in terms of ΔB6s = Δ(σE1/σD2)spont. and of the electrooptical coefficient r63 = σB6/σP3, related to the paraelectric coordinate system. Phenomenological theory explaining the birefringent and electrooptical properties of CAS is developed; since its phase transition is improper ferroelectric, coupling of ΔB6 to both polarization and order parameters is taken into account. It is shown that the electrooptic contribution accounts for only 11% of the ΔB6s value. Optical properties of CAS are found to differ considerably from those of another improper ferroelectric, Gd2 (MoO4)3.